Polymer seals have been used for many years to establish a seal between two components. FIG. 1A is a simplistic depiction of a system 10 comprising a first component 12 and a second component 14 wherein a polymer seal 16 is used to establish a seal between the two components 12, 14. More specifically, the system 10 is designed such that, under the operating conditions of the system 10, a portion of the polymer seal 16 engages a sealing surface 14A on the second component 14. The seal 16 is positioned within a seal recess 18 defined in the first component 12. The first and second components 12, 14 may be stationary to one another during operation or one of the components, e.g., the component 14 may rotate or move relative to the component 12.
Such polymer seals 16 are being employed in an ever-increasing array of applications wherein the seal 16 has to perform its sealing function over a very wide range of temperatures. For example, in some subsea applications, such polymer seals 16 are designed to seal at a temperatures range that may be about −59-343° C. (−75-650° F.). This can be very challenging for the designer of the seal system 10. With reference to FIG. 1A, and in general, an polymer seal 16 is designed such that, under operating conditions, there is a proper amount of designed interference 20D between the seal 16 and the sealing face 14A so that a seal is established. Designing the proper amount of interference 20D takes into account several factors such as the thermal expansion of the components 12, 14 and the seal 16, the spacing between the two components 12, 14, anticipated pressure and temperature fluctuations, etc. Ultimately, the seal 16 must be designed such that if performs its sealing function over the entire design temperature range for the particular application.
This is becoming more problematic as the desired operating temperature ranges for such polymer 16 seals have increased. In general the usefulness of an polymer seal at low temperatures is dependent on whether the polymer material is at a temperature that is above its glass transition temperature (Tg), where it still behave elastically, or below its glass transition temperature (Tg), where the polymer material become relatively harder and relatively less flexible. High pressures are known to shift the glass transition temperature (Tg) of polymer materials which decreases the low temperature sealing performance of the polymer materials. Also, at cold temperatures, the polymer material tends to shrink more than adjacent metal materials due to thermal contraction which causes loss of sealing. In one illustrative application, the seal 16 is designed to operate at a temperature range of 205° C. (400° F.) (high temperature condition) to −18° C. (0° F.) (low temperature condition). As shown in FIG. 11B, if the system 10 is designed such that there is proper sealing interference 20D at the high temperature (205° C.) condition then, as shown in FIG. 1C, there may be insufficient sealing interference 20L at the low temperature (−18° C.) condition, i.e., the seal 16 may be under-squeezed a the low temperature condition, such that the seal 16 will not provide the necessary seal between the two components 12, 14. Conversely, as shown in FIG. 1D, if the system 10 is designed such that there is proper sealing 20D at the low temperature (−18° C.) condition, then, as shown in FIG. 1E, when the seal 16 expands under high temperature (205° C.) conditions, the amount of interference 20H between the seal 16 and the sealing face 14A may be too great, i.e., the seal 16 may be over-squeezed, thereby leading to permanent (non-recoverable) deformation of the polymer seal 16 which results in overall failure of the seal system 10.
The present application is directed to a sealing system comprising a unique shape memory alloy member for use in polymer seal applications that may eliminate or at least minimize some of the problems noted above.